Lightning-boot 2.0

Some changes have been made to lightning-boot so, as with 1.6, I thought a new version number was appropriate and we've now jumped to 2.0 in honour of the git repo, I decided not to fork jburks lightning-boot 1.5 git repo as he has been inactive for quite some time.

This set of changes have added an autoboot feature and load lightning boot from SD menu option, autoboot looks for an empty file called autoboot on the SD card and loads a zImage from the SD card without going through the menu system.

Prerequisites

Didj console
A way to upload lightning boot to the didj, either burn it to nand or use micromon to upload.
lightning boot 2.0 source code git repo
Didj kernel source code 2009 version
git
prebuilt SD kernel and rootfs image kernel_rootfs.tar.gz 35MB

Compilation

grab the kernel source code from the link, untar it to your hard drive, if you haven't compiled a didj kernel before then read any of the 'Build Environments' tutorials on the main wiki page to learn how to set your env vars, then at least start compiling a kernel as lightning-boot will need to grab a few files that are only created at the start of kernel compilation, to do this simply do:

cd Didj-Linux-4222-20090422-1236/linux-2.6.20-lf1000
./install.sh

you don't need to let it compile the whole kernel, as long as its started it will have created the mach-types.h file we need, if it can't find your compiler you may need to edit the makefile and comment out the CC= line.

you might get a couple of warning messages come up, but they don't break anything and the xmodem stuff isn't my code, so I didn't waste much time chasing them down, if anyone knows how to fix them please let me know :)

Installation

If you are running the SD rootfs then you already have my mass storage scripts on the didj, boot into the SD kernel, from the console do:

massenable

and plug in your USB cable, the SD card should automount on your host system.

From your host do:

cp lightning-boot.bin /path/to/FAT/partition
sync

obviously putting the correct path in place of /path/to/FAT/partition.

Flashing lightning-boot to the Didj nand

WARNING the next procedure writes lightning boot to your nand, this could potentially break its ability to boot from NAND as we are writing to the LF1000 SoC expected boot sector, however this is quite unlikely and is recoverable with uart boot if necessary, lastly, even if you do break the nand the device is still usable via uart boot and SD.

I've had to test lightning boot binaries numerous times, quite frankly it got boring making and using md5 checksums every time I wanted to flash it to the didj, the following is my method for flashing the LB binary to the didj.

Unless there are major code updates you will only have to do this once and now that I've added the ability for LB to load lb.bin from the SD card anyone that decides to do any development on lightning-boot-2.0 will only have to flash lightning boot when its absolutely necessary. This might lead to a further feature where LB could autoload a lb.bin file from SD, this would completely remove the need to ever have to touch the didj nand again except for kernel updates.

That's it, read on to see what all the new features do.

Nand and SD partition layout

Through testing I now have 2 kernels on my didj, a standard 2.6.20 didj kernel and an SD based explorer 2.6.31 kernel, both burnt to the nand, the basic layout of my didj nand and sd partitions is as follows:

As you can see there are a couple of additions, the behaviour of 'Boot from NAND normally' has also changed, here's a rundown of what the new/changed options do.

Boot from NAND normally

The way you used to use this option was via setting the /flags/rootfs file to contain the rootfs that you wanted to boot and by the same token the kernel that it would use, for instance, running the following on the cmdline:

echo RFS1 > /flags/rootfs
reboot

Would allow you to reboot into the kernel on mtdblock5 and the rootfs on mtdblock6, as you can see from the nand layout above that would probably cause complications now trying to boot an explorer kernel with didj rootfs. I have made this option react to RFS0/RFS1 flags for the rootfs only, you still get the flexibility of running 2 didj rootfs partitions but from the same kernel (kernel0).

Boot from NAND with SD Kernel and Rootfs

Since making my 'boot kernel and rootfs entirely from SD' hack I have gone one step further in burning the explorer kernel to the didj nand on kernel1 partition, so this option gives you similar functionality to the nand option above for didj kernels, you set the rootfs in exactly the same way as on the didj except you use RFS2/RFS3 to set which way you want to boot the explorer kernel.

Be aware that at this present time the SD rootfs is on a single partition, so whilst you have RFS2/RFS3 you only have a single rootfs, so why bother with RFS3 I hear you cry? Simple answer is that it allows you to choose between 2 kernel boot cmdline configurations (hardcoded into lightning boot, see include/board.h), I have RFS3 setup with debug=1 in the cmdline, this gives feedback to the console (RFS2 boot is almost silent). Having RFS3 also allows us to expand things in the future if for instance you want to dual-boot from SD.

Boot from NAND with custom cmdline

During the testing of the SD kernel and rootfs I only needed to make minor changes to the cmdline, this required me to recompile the kernel or mess around in u-boot. NOT ANYMORE :)

This option allows you to boot the explorer kernel on kernel1 using custom a custom boot cmdline read in from a file on the vfat partition on the SD card, the file is called 'cmdline' and can contain a cmdline with max.255 chars.

Load zImage from SD

This option hasn't actually changed but it should still be explained, fairly obvious from its name that it boots a zImage from the SD card, this option differs from the rest because it actually uses the kernels built in cmdline options (the first 2 options use hardcoded cmdline options in include/board.h in the LB sources).

You would use this option to boot the didj using a 2.6.20 kernel and rfs0/rfs1 partitions, or if you booted an explorer kernel with my SD rootfs hacks enabled it would boot the entire kernel and rootfs from the SD card.

Load lightning boot from SD

This option might seem a bit odd, why would you want to load lightning boot from lightning boot? One simple reason, when you're doing dev work on lightning boot it makes sense to not have to flash it to nand constantly.

It's pretty simple to use, get a copy of lightning-boot.bin, rename it lb.bin (petit fat fs only seems to like 8.3 file naming) and put it on the fat partition of your SD card. This option currently only works from first run of lightning boot, for example, when you first power the didj on or after a reboot this option will work.

If you've already used the option and try to load lightning boot from the newly loaded lightning boot it will overwrite itself and crash. When lightning boot first loads its put in 0x00000000 in ram by the lf1000 internal bootstrap code.

Lightning boot loads everything at 0x01000000, loading lightning boot at 0x01000000 and then trying to load anything else will cause it to lightning boot to load the binary over itself and crash, so loading of lightning boot from within itself is done at 0x00800000, this is why it currently works the first time through. This will be addressed in a future update, although its fairly unlikely that you'll need to reload lightning boot 3 times without going into the kernel.

Autoboot zImage from SD

this option allows the user to autoboot a kernel zImage from SD, removing the need for user intervention,

You may have noticed this this feature doesn't appear on the menu itself. To use the feature simply create an empty file called autoboot on the fat partition, lightning boot will automatically boot the zImage from SD, to disable this feature simply delete the file from the fat partition.

How does all this fit together

We now have similar flexibility to boot a 2.6.20 kernel with either Didj root filesystem as you normally would with LB1.4/1.5.

We have the ability to burn a modified 2.6.31 explorer kernel to your nand that boots its root filesystem from SD, you also have a debug mode that it will boot into, so that gives you similar functionality to option 1 and the fastest possible boot time.

We can now test custom cmdline configs for 2.6.31 kernels burnt to nand, this allows for faster development times as the vfat partition can easily be accessed to allow you to quickly change the boot cmdline.

The vfat partition access allows you to update the kernel and/or lightning-boot quickly and easily without having to remove the SD card. To give you some idea, it takes around 10seconds to compile the lightning boot, upload it to the didj, flash and reboot into the new lightning boot.

We now have the ability to completely boot from SD card, this means that you can safely test a kernel without EVER having to touch your nand (apart from the lightning-boot update itself of course).

We now have better recovery options, booting entirely from SD means that failed nand is no longer an issue, as long as UART boot works you can boot a didj even if the the nand is totally trashed, using micromon and lb1.6(untested).

Now that we can load lightning boot from within itself we can test lightning boot updates without having to burn to nand until we are satisfied that it works properly, this has the obvious advantage of not needing uboot to recover from failed code changes and less nand write cycles.

It also gives us the opportunity to start testing emerald boot in the same manner by simply renaming emerald-boot.bin to lb.bin on the sd card. I'll probably add another menu option for loading emerald boot in its own right in the near future.

Lastly, now that both the didj and explorer can use the same kernel and mostly the same rootfs we can push development for both machines in the same direction with minimal impact.

Anything I've missed?

Yeah, probably, there wasn't much of a plan for lb1.6 or 2.0, however I think the options I've chosen and implemented are reasonable for now. I will probably add a couple more options, 'custom cmdline for didj kernel' and 'custom cmdline for zImage from SD' seem like sensible additions.

I've made this version of lightning-boot more geared towards the 2.6.31 explorer kernel, if you are just using normal didj kernels and rootfs lightning-boot 1.6 probably isn't for you :)

Now that we have full access to a 2.6.31 kernel and rootfs on a didj we can all move up to the much better kernel, so the didj and explorer development can take the same path, apart from usb host, reduced ram and touchscreen they are essentially the same machine.

NO WARRANTY implied or given, if it breaks your stuff, I want pictures :) I have tested lightning-boot 1.6 on 2 didj's so far, neither have had any issues with losing data, all partitions are sound.

it would probably be sensible at some point in the future if you are SD booting to create a third partition for rootfs recovery/updates/general linux filesystem based storage, I plan to add this myself to a fuller tutorial in the future, this would give much more flexibility over the vfat partition which has the obvious windows file limiations seen on linux.

lightning-boot has increased in size, best burnt to nand, its now > 16KB so it can no longer be used via the normal uart boot method, however, using jkents excellent micromon you shouldn't have any issues uart booting it that way instead.